Received the following comments from Paul Poletti re: hide glue and bridge caps. He suggested I post these on the list. I will forward any replies. Stephen Birkett (Fortepianos) Authentic Reproductions of 18th and 19th Century Pianos Waterloo, Ontario, Canada tel: 519-885-2228 fax: 519-763-4686 ************************FORWARDED MESSAGE******************* Just a quick reply to the [hide glue / bridge cap thread]. Anybody who says stuff like this [i.e. susceptibility to atmospheric moisture etc.] about hide glue is only demonstrating their complete ignorance of the topic, both in terms of practical experience and technical knowledge. They should read some industrial technical reports on adhesives and their applications. Hide glue is still used for many applications today because it is the best glue for that specific use. When used properly, it is stronger than PVA's (Titebond), does not creep when cold like all PVA's can, and is no more susceptible to atmospheric moisture. To say that hide glue can come apart from atmospheric moisture is really only to make evident that fact that one has never done any professional restoration work in which you have to take apart hide glue joints with soaking or steaming. No one who has would believe this nonsense for an instant: well-made hide glue joints are exceedingly stubborn things. We took out the treble block of a piano from 1828: it took three days of injecting hot water and alcohol into the joint, finally had to be broken open with reverse clamps, and there was lots of tear-out. And this in a piano that had sat on its back in water so long that the spine rotted almost completely away. The same piano also has a bent laminated bridge (two pieces) that is so well glued you can hardly find the seam. People can go ahead and believe this sort of nonsense about hide glue if they want a good excuse for never really mastering their trade. The use of hide glue, like any professional tool or material, has to be learned, but once you learn it, it is amazing stuff. Its flexibility in open/setting times (depending on grade and mix) and its eternal reversibility make it the best. It is not idiot-proof. You have to know what you're buying and how to use it. It is a professional product for professional woodworkers. Amateurs should stick to the plastic yellow and white stuff. The only bridge cap I've had any experience with was on a c.1850 French upright. The thing had been restrung with modern wire, overly strung, and the pins where tearing through the wood from the extra tension. I removed the cap and found that the splitting was running through the lower laminates as well. But NOT along the glue lines. I've never seen a cap on an earlier piano, no matter what the manner of bridge bending. I suspect capping was done to provide a smooth surface for boring the pin holes, since the glue seams could influence the run of the drill bit, making it hard to accurately control the position of any pin which must stand almost right on top of a glue seam. In earlier bridges, the treble bend is made by sawing the bridge down its middle to about middle c, and then regluing it on a bent form. Since the seam runs down the middle, no pin ever needs be close to it, thus no cap. By the way, I've seen many such bridges, but I've NEVER seen one in which the central glue line is failing from "atmospheric moisture". Paul Poletti, Poletti and Tuinman Fortepianos, Utrecht, The Netherlands
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